1. Field of the Invention
The present invention relates generally to the field of bookbinding and in particular to sheets which have been conditioned to enhance binding using thermal adhesive binder strips.
2. Description of Related Art
Bookbinding apparatus have been developed which permits stacks of sheets to be bound using thermally activated adhesive binder strips. Such binder strips are typically applied using relatively low cost desktop binding machines such as disclosed in U.S. Pat. No. 5,052,873, the contents of which are also incorporated herewith by reference. Referring to the drawings, FIG. 1 shows a binder strip 20 disposed adjacent the insertion point 30A of a conventional binding machine 30. A user first inserts a stack of sheets 32 to be bound in an upper opening of the machine. Controls 30B are then activated to commence the binding process. The binding machine operates to sense the thickness of the stack 32 and indicates on a machine display 30C the width of binder strip 20 to be used. Typically, three widths can be used, including wide, medium and narrow. The binder strip includes a flexible substrate 20A having a length that corresponds to the length of the edge of the stack 32 to be bound and a width somewhat greater than the thickness of the stack. A layer of heat-activated adhesive is formed on one side of the substrate, including a low viscosity, low tack central adhesive band 20C and a pair of high viscosity, high tack outer adhesive bands 20B.
Once the user has selected the binder strip of appropriate width, the user manually inserts the strip 20 into the strip loading port 30A of the machine. The end of the strip, which is positioned with the adhesive side up, is sensed by the machine and is drawing into the machine using an internal strip handling mechanism. The machine then operates to apply the strip to the edge of the stack to be bound. The strip is essentially folded around the edge of the stack, with heat and pressure being applied so as to activate the adhesives. Once the adhesives have cooled to some extent, the bound book is removed from the binding machine so that additional books can be bound. FIG. 2 depicts a partial end view of the bound stack 32. As can be seen, the substrate 20A is folded around the bound edge of the stack. The high tack, high viscosity outer adhesive bands 20B function to secure the strip to the front and back sheets of the stack. These sheets function as the front and rear covers and can be made of heavy paper or the like. The central, low viscosity adhesive 20C functions to secure the individual sheets of the stack by flowing up slightly between the sheets during the binding process.
Although the above-described binding technique provides a reliable bind in most applications, problems arise when the sheets of the stack have special coatings. Such coatings are applied to the sheets for various purposes to enhance the characteristics of the sheet, such as improving the ability of the sheet to receive special printing inks. In any event, such coatings very frequently prevent the central adhesive 20C from adhering adequately to the individual sheets of the stack. This results in an unsatisfactory bind where sheets frequently separate from the stack.
In order to address the above-described problem, apparatus were developed for conditioning the stack of sheets prior to binding. This method and apparatus are disclosed in application Ser. No. 10/775,039, filed on Feb. 9, 2004 and entitled “Stack Conditioning Apparatus and Method for Use in Bookbinding”. That application Ser. No. 10/775,039, the contents of which are hereby fully incorporated into the present application by reference, is assigned to the assignee of the present application. Referring again to the drawings, FIGS. 3 and 4 depict one embodiment of the prior art conditioning apparatus. The apparatus includes a housing 36 of a size suitable for desktop use. A clamping platen 38 is mounted for lateral movement on a pair of linear guide rails 48A and 48B. Platen 38 includes a vertical member 38A for holding a stack of sheets (not depicted in FIGS. 3 and 4) to be conditioned. A stack clamping carriage 44 is also mounted on the guide rails 48A and 48B for lateral movement. The clamping carriage 44 and platen 38 are coupled together by pair of heavy springs (not depicted) that apply a clamping force to a stack disposed in the cavity 45.
Clamping carriage 44 carries a pair of drive nuts 42A and 42B which receive respective lead screws 40A and 40B. The lead screws 40A and 40B are driven together in either direction by an indexing stepper motor 50. A drive belt (not depicted) couples the motor 50 output to the two lead screws. A stack support member 46 is cantilevered mounted below the clamping carriage 44 and clamping platen 38 and includes a surface 46A. The carriage 44, platen 38 and support member surface 46A form a clamping cavity 45 for receiving a stack of sheets to be conditioned. A multiplicity of piercing blades 52, one of which is depicted in FIG. 8, are supported on respective blade holders 54. In the exemplary conditioning apparatus, there are a total of twelve separate blade holders 54, with the blades 52 being aligned along a common axis. As will be explained in greater detail, the blades function to pierce the edge of each individual sheet of the stack. The use of multiple piercing blades 52, which are driven into the stack at differing times, function to reduce the amount of driving force needed and thus permit the use of a smaller drive motor and other related components. This feature also reduces noise and vibration. FIG. 5 shows four of the twelve blade holders 54 and the associated structure. FIGS. 6 and 7 show further details of the individual blade holders 54.
The piercing blades 52, which are preferably made of ceramic, are each provided with several individual piercing elements 52A (FIG. 8). In the exemplary piercing blade of FIG. 8, there are eleven piercing elements. Each piercing element 52A terminates in a wedge that defines a relatively sharp cutting edge 74 which has a width W of typically 0.025 inches. The spacing P between the edges is typically 0.025 inches. The use of multiple, spaced apart, piercing elements 52A has been found to produce superior results and to further reduce the required driving force. The piercing blades 52 are each approximately one inch in length thereby providing a total length of twelve inches so that stacks with edges of up to twelve inches can be accommodated.
Each piercing blade 52 is secured in a recess 54C formed in the blade holder 54. A blade support block 68 and associated set screw 66 function to hold the blade in place and permit easy blade replacement. The blade holders 54 each have rear openings 54A for pivotally mounting the holder on a common pivot shaft 64 (FIG. 5). The blade holders 54 are driven by a common camshaft 58 having a separate cam surface 58A for each of the blade holders. The respective cam surfaces 58A each engage a cam follower bearing 56 mounted on each of the blade holders. Although not shown, each blade holder 54 includes a return spring connected to hold the cam follower bearing 56 down on to the cam surface 58A. These springs assist in retracting the blades 52 from the stack and force the cam follower bearing 56 to follow the contours of the cam surfaces. The cam surfaces 58A are configured so that, for each complete rotation of the camshaft 58, each of the blade holders 54 will cause each of the piercing blades 52 to reciprocate between a withdrawn position and a piercing position. The amount of blade movement above the surface 46A, which defines the location of the stack edge to be conditioned, is typically between 0.010 and 0.030 inches.
Given the substantial distance between pivot shaft 64 and the location of the blade 52 on the holder, this reciprocating blade movement will fall in a piercing plane that is substantially orthogonal to the stack receiving surface 46A. As used herein, blade movement falls substantially within a piercing plane if the angle of movement is within ±25 degrees of the angle of the plane. Preferably, each of the cutting edges 74 of all of the twelve blades 52 in the exemplary conditioning apparatus fall within this piercing plane. Further, as used herein, a plane defined by at least by that region of the sheet near the edge of the stack to be conditioned is said to be substantially coincident with a plane such as the piercing plane if all of the angles between the respective planes are each within ±25 degrees. As will be explained in greater detail, each sheet of the stack, at least in the region near to edge of the stack being conditioned, will define a sheet plane that will pass through, and be substantially coincident with, this piercing plane. During this relative movement, the blade 52 will be activated at a frequency to ensure that each sheet of the stack is pierced at least once. Note that the stack front and rear cover sheets are secured in place by the outer adhesive bands 20B (FIG. 2) and thus do not rely upon the central adhesive 20C. Such cover sheets do not require conditioning but it does no harm to condition the edges of the cover sheets.
Operation of the prior art conditioning apparatus will now be described in connection with FIGS. 3 and 4. Prior to actuation of a control panel switch (not depicted), the clamping platen 38 and clamping carriage 44 are in a home position for receiving a stack of sheets to be conditioned. In this home position, the stack support member receiving surface 46A is exposed to receive a stack to be conditioned. A pair of relatively strong springs (not depicted), disposed along the respective linear guide rails 48A and 48B, are couple between the platen 38 and carriage 44 and operate to pull the platen towards the carriage. A stop (not depicted) prevents the clamping platen 38 from being pulled closer to the platen 38 than shown in FIGS. 3 and 4. A user first places the stack to be conditioned in the clamping cavity 45, with the stack edge to be conditioned resting on surface 46A. The user then actuates the control panel switch (not depicted) causing stepper motor 50 to drive the clamping carriage 44 by way of the two lead screws 40A and 40B. The direction of movement is towards the stack and the clamping platen 38 on the other side of the stack. The stack is gripped between the extended surfaces associated with clamping carriage 44 and platen 38 to within 0.030 to 0.050 inches from surface 46A thereby preventing the reciprocating blades from contacting the carriage and platen.
Eventually, the driven clamping carriage 44 will contact the stack and will proceed to move the stack and the clamping carriage 38 together, as represented by arrow 75 shown in FIG. 9. Carriage 44 will then start to drive the stack 70 off of the stack support member 46 as shown in FIG. 9 and over the piercing blades 52. While this is occurring, the two springs coupling the carriage 44 and platen 38 together will continue to apply a substantial compression force to the lower portion of the stack 70. This causes the stack 70 to form an essentially solid block so that the individual sheets support one another and are not deflected during the conditioning process.
While the stack 70 is being driven over the piercing blades 52 at a controlled rate, the blades 52 are caused to reciprocate by blade drive motor 62 and the camshaft 58. This reciprocating movement is represented by arrow 76. Assuming that the thickness of the individual sheets of the stack 70 is N inches, the stack is driven in incremental steps of N inches or less. After each of these steps, the piercing blades 52 are reciprocated between the withdrawn position and the piercing position. This insures that each individual sheet of the stack is pierced. Preferably, each advance is only a fraction of the sheet thickness N to add a margin of safety since it is important that each sheet (excluding front and rear cover sheets) be pierced. An advance of ½ of N has been found satisfactory. Thus, for a typical sheet thickness of 0.004 inches, the stack is advanced 0.002 inches prior to each piercing. Stepper motor 50 and drive motor 62 are synchronized to ensure this relationship. Thus, at the end of every 0.002 inches of stack travel, the stepper motor 50 pauses and the drive motor 62 causes camshaft 58 to be rotated 360 degrees. This causes each of the twelve blade holders 54 to be sequentially driven so that each of the twelve blades 52 sequentially pierces the sheets of the stack 70. As previously noted, the blades 52 are set to pierce the sheets of the stack in a typical range of between 0.010 and 0.030 inches.
Once the inner surface of the clamping carriage 44 has reached the piercing plane defined by the reciprocated motion of the individual piercing elements 52A of the twelve piercing blades 52, the stepper motor stops advancing the stack 70. The next step is to return the stack to the home position so that the conditioned stack can be removed. FIG. 10 illustrates a portion of the conditioned stack 70. As can be seen, each of the individual sheets 70A is pierced so that the ends of the sheet are split by the cutting edges 74 of the wedge-shaped piercing elements 52A (FIG. 8). When this occurs, there is a tendency for the fibers of the sheet to tear so that a split is formed in the paper in the region intermediate the points at which adjacent ones of the piercing elements 52A enter the sheet edge.
Although FIG. 10 shows a conditioned stack with splits 72 formed in each sheet, these results are somewhat idealized. FIGS. 11A, 11B and 11C show more typical examples of individual sheets of a stack that have been conditioned. The example of FIG. 11A, a true split 72A is created in a sheet 70A, similar to the splits shown in FIG. 10. This results in a pair of opposing surfaces generally being exposed. In the example of FIG. 11B, it can be seen that sheet 70A has been pierced twice by the piercing element exposing a pair of surfaces 72B. A further example is shown in FIG. 11C where a sheet 70A is pierced in a location such that, rather than forming a split, a single surface 72B is exposed. An individual sheet may have variations of each of these examples along the entire edge of the sheet. Preferably, at least 10 percent and preferably at least 50 percent of the linear length along the edge of the sheets is pierced or torn by the individual piercing elements 52A, to achieve a reliable bind.
In all of the examples of FIGS. 11A-11C, a significant amount of surface area of the fibrous center of the coated paper sheet 70A has been exposed. This is due in part to the fact that the above-described reciprocating action of the piercing blades 52 tends to result in relatively large exposed surfaces that are roughly parallel to the plane of the sheets 70A. These types of exposed surfaces, which are reliably formed on each sheet of the stack, cannot be achieved using prior art methods that somewhat randomly apply abrading action to the stack edge. FIG. 12 shows a portion of a stack conditioned bound using a conventional binder strip 20 and conventional binding machine 30 as depicted in FIGS. 1 and 2. It can be seen that the low viscosity adhesive 20C is adhering to the exposed inner fibrous surfaces of each of the individual sheets. This results in a bound volume where each individual sheet, whether coated or not, is securely held in place.
As previously noted, the very lowest portion of stack 70 is not clamped during the conditioning process thereby enhancing the results of the conditioning. FIG. 14 shows a prior art modification to the lower portion of the FIG. 9 clamping platen 38 and clamping carriage 44 which provides an optimum clamping force for holding the ends of the stack in place. A lower portion of the stack 70, displaced from the end by a significant distance, is gripped securely by a pair of opposing rigid clamping sections 100A and 100B. Although clamping members 100A/100B provide significant compression force, they are sufficiently displaced from the lower end of the stack so as not to interfere with the piercing operation itself. A pair of additional opposing clamp sections 104A and 104B are pivotally supported at the top of the clamp sections by respective hinge pins 108A and 108B. Respective springs 110A and 110 B trapped between respective portions of the clamp sections 100A/100B and the respective pivoting clamp sections 104A/104B to provide a small compression force to the pivoting clamp sections. The springs cause the lower portion of the clamp sections 104A/104B to exert a minimal force needed to hold the ends of the sheets together for the piercing operation. As the piercing operation takes place, the lower end 71 of the stack will tend to expand or fan out due to the splitting of the sheets, with clamps sections 104A and 104B functioning to swing out to accommodate the thicker end of the stack. Note that the lower edges of the pivoting clamp section 100A/100B are disposed a small distance from the stack edge 71 so that the lower clamp section edges will not be struck by the piercing elements 52 of the piercing blade.
The previously described apparatus and method of conditioning a stack of sheets represented a substantial improvement in the art of permitting thermal binding of essentially all types of paper. Nevertheless, further advances are desired. The present invention provides such advances in the art as will become apparent to those having ordinary skill in that art upon a reading of the following Detailed Description of the Invention together with the drawings.